A high voltage DC breaker apparatus may be arranged in a high DC voltage carrying system, for example in Voltage Source Converter based multi-terminal HVDC (High Voltage Direct Current) networks where fast-rising DC fault currents must be interrupted quickly at high voltages. Such faults may be line-to-line faults or line-to-ground faults, i.e. short-circuits of the DC conductor to earth. By high voltage is here meant a voltage 10 kV (and often a voltage of several hundreds of kV) with respect to ground.
In one type of known such breaker apparatuses said arrangement configured to obtain zero-crossing of a fault current through the interrupter comprises a passive LC-circuit generating an oscillation of fault current through the interrupter with the aim to obtaining a zero-crossing of the fault current. A disadvantage of using such an arrangement is the uncertainty as to when zero-crossing of the current will actually occur, which results in a risk of failing the arc extinguishing window when interruption of the current is possible, so that interruption of the fault current may not be reliably ensured.
Another type of known high voltage DC breaker apparatuses uses a said arrangement having a pre-charged capacitor connected in parallel with the mechanical interrupter for obtaining current-zero-crossing of the fault current. However, this solution is comparatively costly, since a large capacitor as well as a separate high voltage charging device for charging the capacitor are needed.
U.S. Pat. No. 5,517,378 discloses a high voltage DC breaker which has two mechanical breakers adapted to be traversed by the line current and to be opened for breaking the current. A capacitor is connected in parallel with the series connection of the breakers. A semiconductor member is connected in parallel with a first one of the breakers. Upon opening of the breakers, a control member controls the semiconductor member such that a zero crossing of the current through the second breaker is obtained, whereby the line current is commutated over to the capacitor.